I'm having temp problems and need advice

[Bogertophis]

...Also the tank is a 20 gallon long, does that change anything? Should I put the UTH closer to the middle but not directly so the heat can reach both sides?

You always need to leave an unheated area for safety & for proper thermoregulation by your snake, so usually the UTH is at "one end", but in a chilly room, it might help a little if it was closer to, but not at, the middle. Also, I would suggest insulating the back & sides of the tank, also the lower part of the front, & part of the bottom except for under & near the UTH; insulation will help keep the heat in, but it's still going to be hard (if not impossible) to overcome a room that's too cold.